1. Field of the Invention
The invention concerns a magnetic field sensor of the kind having two flux concentrators and a sensor for measuring a magnetic field, wherein the flux concentrators are separated by an air gap.
2. Description of the Prior Art
U.S.-american patent specification U.S. Pat. No. 474 9939 discloses a magnetic field sensor for measuring the energy transported through an electric conductor. The magnetic field sensor has a vertical Hall element and two magnetic flux concentrators. The flux concentrators and an external yoke form a magnetic circuit of ferromagnetic material, in the air gap of which the Hall element is disposed.
The flux concentrators are of a configuration such as to reduce in width towards the Hall element in order to produce a magnetic field which is as high as possible in the air gap in relation to the current flowing in the conductor, and thus to achieve a high level of sensitivity. The geometry of the flux concentrators is optimised in such a way that the magnetic flux outside the air gap, that is to say the leakage field component, is as small as possible so that the linearity of the magnetic field sensor is not adversely affected by saturation effects of the flux concentrators. The minimum possible width of the air gap is limited in a downward direction by the dimensions of the Hall element disposed in the air gap.
Although it is possible with horizontal Hall elements further to reduce the dimensions of the air gap, as however the flux concentrators in principle must be of a different configuration in order to pass the magnetic field through the Hall element, such an arrangement is sensitive to interference fields which act on the Hall element in a perpendicular direction.